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Some of you may have seen my recent hair-pulling thread, in which my car intermittently would not start (no starter motor operation), and then finally came to the point of not starting at all unless the battery had been disconnected & reconnected since the previous shutdown.

I followed what seemed to be the best bet and ordered a new ignition switch electrical portion: 4A0 905 849 B, as well documented in the DIY for this job. Luckily, the eBay shipment arrived on Thursday, so I crawled under the dash yesterday, armed with my very short screwdriver. Upon removing my old switch, it was obvious they were different. I rechecked the new switch number. Yep, its different from the old one, but I expected a superceded part .... and it fit. Problem is, in the installed, key off position, this switch is electrically ON .... something one does not notice until all buttoned up, out of the car, and reconnecting the battery.

A trip to the local Audi dealer this morning confirmed that 4A0 905 849 B (black in color) is not electrically compatible with my car (ON when it should be OFF). It also yielded an exact replacement for my old switch, 4B0 905 849 (white in color) .... at $85. Well, it would be worth it, of course, to get the car fixed.

This time I was savvy enough to leave the air duct off until I checked things out. Reconnected the battery, car started right up, wife came out to celebrate. I then turned the car off, and attempted a restart. No go. Same exact symptoms.

Finally, I give up and take the car to my Indy shop. After hearing the symptoms, he had an immediate diagnosis: bad immobilizer computer. I tend to give him credence, since he knows he cannot do the repair (and, because I've known him for years). New computer will have to be installed at dealer since all keys will have to be re-mated to it after installation.

Monday, I guess I will pay the price for all those posts in which I have pointed out that my car has required no unscheduled maintenance at the dealer in the 4 years / 50K miles I have operated it. So, I'm bummed, but still very much in love and not at all dissatisfied with my 996.

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Finally, I give up and take the car to my Indy shop. After hearing the symptoms, he had an immediate diagnosis: bad immobilizer computer. I tend to give him credence, since he knows he cannot do the repair (and, because I've known him for years). New computer will have to be installed at dealer since all keys will have to be re-mated to it after installation.

Monday, I guess I will pay the price for all those posts in which I have pointed out that my car has required no unscheduled maintenance at the dealer in the 4 years / 50K miles I have operated it. So, I'm bummed, but still very much in love and not at all dissatisfied with my 996.

Hennessy Porsche in north Atlanta confirmed the diagnosis of bad immobilizer computer .... officially known as the Theft Control Unit.

One little catch .... when that is replaced, none of the existing keys are mated to it, and, of course, I no longer have the bar code tags that came with my 2 alarm keys. I never had the one that came with my pre-owned car. Result: the valet key could be re-mated, as it does not interface with the alarm system & has no bar code, but I had to buy a new key head for my every day key. ( I settled for one key that would work the alarm, instead of the two I had before).

For those who have contributed tales of dealer rip offs in selling / mating keys, Hennessy charged a retail of 174.38 (PCA discounted to 157) for the key head, but that INCLUDED programming the car to accept it. Bottom line is that its not that much more than the $75 I paid 3+ years ago for a key head on eBay combined with $50 for Hennessy to program it.

Edited by Kim
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